diff --git a/autoload/vital/__vital__/Web/JSON.vim b/autoload/vital/__vital__/Web/JSON.vim
index c7e837259..b62f0d789 100644
--- a/autoload/vital/__vital__/Web/JSON.vim
+++ b/autoload/vital/__vital__/Web/JSON.vim
@@ -180,9 +180,6 @@ function! s:_encode(val, settings) abort
       return 'false'
     elseif s:const.null == a:val
       return 'null'
-    else
-      " backward compatibility
-      return string(a:val)
     endif
   elseif t == 3
     return s:_encode_list(a:val, a:settings)
@@ -200,9 +197,8 @@ function! s:_encode(val, settings) abort
     return get(s:special_constants, a:val)
   elseif t == 10
     return s:_encode_list(s:bytes.from_blob(a:val), a:settings)
-  else
-    return string(a:val)
   endif
+  throw 'vital: Web.JSON: Invalid argument: ' . string(a:val)
 endfunction
 
 " @vimlint(EVL102, 1, l:ns)
diff --git a/test/Web/JSON.vimspec b/test/Web/JSON.vimspec
index 1f15aa335..415af4241 100644
--- a/test/Web/JSON.vimspec
+++ b/test/Web/JSON.vimspec
@@ -308,5 +308,31 @@ Describe Web.JSON
       Assert Equals(JSON.encode(0z), '[]')
       Assert Equals(JSON.encode(0zFF.00.ED.01.5D.AF), '[255,0,237,1,93,175]')
     End
+
+    It throws exception when encodes funcref
+      let Funcref = function('get')
+      Throws /^vital: Web\.JSON: Invalid argument: / JSON.encode(Funcref)
+    End
+
+    It throws exception when encodes job
+      if !has('job')
+        Skip no available job type.
+      endif
+      if has('win32')
+        let job = job_start('cmd /c ""')
+      else
+        let job = job_start('true')
+      endif
+      Throws /^vital: Web\.JSON: Invalid argument: / JSON.encode(job)
+    End
+
+    It throws exception when encodes channel
+      if !has('channel')
+        Skip no available channel type.
+      endif
+      let ch = ch_open('localhost:12345', {'waittime': 0})
+      silent! call ch_close(ch)
+      Throws /^vital: Web\.JSON: Invalid argument: / JSON.encode(ch)
+    End
   End
 End